Technical Field
The present disclosure relates to a motor drive device.
Related Art
As a blower motor employed to convey air in a vehicle air conditioner, sometimes brushless DC motors are employed in which a rotor configured by a permanent magnet tracks a rotating magnetic field generated by a stator, provided along the circumferential direction of the rotor, and rotates. Since, unlike brushed DC motors, brushless DC motors do not have a sliding configuration, power consumption is low compared to brushed DC motors, and are compatible with faster rotation speeds.
When the number of revolutions are increased in the motor, the load on the motor and a motor drive device that drives the motor increases. In the motor drive device of the brushless DC motor, for example, the load on the motor and the motor drive device is detected from a power source current value detected by a current sensor, provided between an inverter circuit generating voltage applied to the motor by switching and a battery that is a power source. Control is then performed to lower a duty ratio of voltage applied to the motor in cases in which there is a possibility of overload.
However, spikes in noise are generated sporadically in the current between the power source and the inverter circuit, such that there is a possibility that the detection of the current sensor is affected by the noise.
Japanese Patent Application Laid-Open (JP-A) No. 2011-50202 describes an electric motor drive device in which sporadic noise is eliminated by processing a signal output from the current sensor using a low pass filter to smooth the signal.
However, in the electric drive device described in JP-A No. 2011-50202, there is a possibility of significant error, such that the detected current value is lower than the actual current value, due to high frequency components of the signal being excessively eliminated by the low pass filter. In cases of significant error such that the detected current value is lower than the actual current value, strict determination criteria for overload and prioritized protection of the motor and drive device are required. There is accordingly a possibility that the duty ratio of current applied to the motor is more frequently lowered, impairing efficient operation of the motor. There is also a possibility that the product incurs an increase in cost due to mounting a filter such as the low pass filter to the circuit.